The process of this invention relates to the preparation of 2-hydroxybenzenesulfonamide by a three step process beginning with 2,4-dichlorophenol. More specifically the process of this invention relates to treating 2,4-dichlorophenol with chlorosulfonic acid followed by treatment with ammonia and finally dehalogenation to form 2-hydroxybenzenesulfonamide.
The sulfonamides described in European patent application No. 44,212 (1/20/82) are herbicides showing very high activity. Such compounds have been difficult to prepare. The ready availability of 2-hydroxybenzenesulfonamide (A), would simplify the preparation of these compounds but present routes to (A) involve several steps which proceed in low yields. All known methods to (A) have started with 2-nitrophenol and involve a 6-step sequence similar to that described in J. Chem. Soc., 2903 (1958) and shown in Equation 1. ##STR1## The overall yield for this route was improved to 14% as described in Chem. Ind. (London) 888 (1972). Alternately, sulfonates have been used as protecting groups in place of the benzyl group.
Published European patent application No. 44 807 (1/27/82) describes the preparation of (A) via the procedure outlined in Equation 2. ##STR2## The starting 2-alkoxybenzenesulfonamides were apparently prepared via a diazotization and coupling sequence similar to that described in Equation 1.
One might approach the synthesis of (A) beginning with phenol, introducing the ortho sulfonamide group via a sulfonation step. Several attempts at this using a variety of conditions and sulfonating reagents all provided a mixture of the ortho and para isomers, which are difficult to separate. The para isomer nearly always predominates (H. Gerfontain, "Mechanistic Aspects in Aromatic Sulfonation and Desulfonation," 1968, pp. 96-102). Thus, one skilled in the art would not pursue this avenue to (A).
A synthetic route is described in J. Amer. Chem. Soc., 82, 1135-1138 (1960) wherein 2-amino-4,6-dichlorobenzenesulfonamide is dehalogenated to 2-aminobenzenesulfonamide (B). If one were to attempt to incorporate a similar step into a route to (A), the preparation of 2-hydroxy-4,6-dichlorobenzenesulfonamide would be necessary. The chlorosulfonation of 3,5-dichlorophenol, however, occurs in the position para to the oxygen to give 2,6-dichloro-4-hydroxybenzenesulfonyl chloride, as described by Cremple and Crongi, Phosphorus and Sulfur, 6, 413 (1979). Thus, a scheme paralleling that described for (B) would provide 4-hydroxybenzenesulfonamide rather than (A).
The chlorosulfonation of 2,4-dichlorophenol is also described in the above reference, as is its subsequent amination to prepare 2-hydroxy-3 5-dichlorobenzenesulfonamide. Dehalogenation of aromatic halides is generally known in the art, as described for 2-amino-4,6-dichlorobenzenesulfonamide above; however, dehalogenation of halo-2-hydroxybenzenesulfonamides to provide (A) has not been previously reported.
The current routes to (A) involve the six step, low yield, volume inefficient process involving diazotization chemistry and/or expensive reagents such as boron tribromide (BBr.sub.3). Due to the variety of sulfonamides available using (A) as an intermediate, any improvement in its preparation is desirable. In particular, a route in which (A) was provided in a form readily convertible to derivatives such as 2-alkanesulfonyloxy-, 2-alkyloxy-, 2-alkenyloxy-, 2-alkynyloxy-, or 2-acyloxy-benzenesulfonamides would be especially useful.